In addition to the standard certificate fields, ''certificate extensions'' allow addition of custom data to digital certificates.

Exception encountered, of type "Error"
[5fa64745] /index.php?diff=prev&oldid=5251&title=An_Overview_of_Public_Key_Infrastructures_%28PKI%29 Error from line 434 of /var/www/techotopia/includes/diff/DairikiDiff.php: Call to undefined function each()
Backtrace:
#0 /var/www/techotopia/includes/diff/DairikiDiff.php(544): DiffEngine->diag()
#1 /var/www/techotopia/includes/diff/DairikiDiff.php(344): DiffEngine->compareSeq()
#2 /var/www/techotopia/includes/diff/DairikiDiff.php(227): DiffEngine->diffLocal()
#3 /var/www/techotopia/includes/diff/DairikiDiff.php(721): DiffEngine->diff()
#4 /var/www/techotopia/includes/diff/DairikiDiff.php(859): Diff->__construct()
#5 /var/www/techotopia/includes/diff/DairikiDiff.php(980): MappedDiff->__construct()
#6 /var/www/techotopia/includes/diff/TableDiffFormatter.php(194): WordLevelDiff->__construct()
#7 /var/www/techotopia/includes/diff/DiffFormatter.php(140): TableDiffFormatter->changed()
#8 /var/www/techotopia/includes/diff/DiffFormatter.php(111): DiffFormatter->block()
#9 /var/www/techotopia/includes/diff/DifferenceEngine.php(881): DiffFormatter->format()
#10 /var/www/techotopia/includes/diff/DifferenceEngine.php(797): DifferenceEngine->generateTextDiffBody()
#11 /var/www/techotopia/includes/diff/DifferenceEngine.php(728): DifferenceEngine->generateContentDiffBody()
#12 /var/www/techotopia/includes/diff/DifferenceEngine.php(662): DifferenceEngine->getDiffBody()
#13 /var/www/techotopia/includes/diff/DifferenceEngine.php(632): DifferenceEngine->getDiff()
#14 /var/www/techotopia/includes/diff/DifferenceEngine.php(453): DifferenceEngine->showDiff()
#15 /var/www/techotopia/includes/page/Article.php(797): DifferenceEngine->showDiffPage()
#16 /var/www/techotopia/includes/page/Article.php(508): Article->showDiffPage()
#17 /var/www/techotopia/includes/actions/ViewAction.php(44): Article->view()
#18 /var/www/techotopia/includes/MediaWiki.php(490): ViewAction->show()
#19 /var/www/techotopia/includes/MediaWiki.php(287): MediaWiki->performAction()
#20 /var/www/techotopia/includes/MediaWiki.php(714): MediaWiki->performRequest()
#21 /var/www/techotopia/includes/MediaWiki.php(508): MediaWiki->main()
#22 /var/www/techotopia/index.php(41): MediaWiki->run()
#23 {main}